Programming Training

1. Programming Training Main Points: - Strings and Characters in C.

2. Working with Strings Strings can be defined as: 1. a sequence of characters in between “…”. 2. an array of characters in which the last char is ‘\0’. String can be declared in two ways: 1. as an array e.g. char str [200];  str does not change 2. as “pointer” e.g. char * str;  str can change Reading a string can be done in several ways: printf(“%s”, &str);  read the string until the first space. gets(str);  read the whole string including spaces.

3. Operations with Strings Operations on strings are done with function from string.h. strcmp(str1,str2)  compares two strings. strlen(str)  gives the length of str strcpy(str1, str2)  copy str2 to the str1 strstr(str1, str2)  find the occurrence of str2 in str1 etc.

4. Working with Characters char is the C type for characters which can be letters, digits, special characters etc ctype.h is library to test the nature of chars. int isalnum(int c); int isalpha(int c);int iscntrl(int c); int isdigit(int c);int isgraph(int c); int islower(int c);int isprint(int c); int ispunct(int c);int isspace(int c); int isupper(int c);int isxdigit(int c); int tolower(int c); int toupper(int c);

5. Working with Characters char is the C type for characters which can be letters, digits, special characters etc ctype.h is library to test the nature of chars. int isalnum(int c); int isalpha(int c);int iscntrl(int c); int isdigit(int c);int isgraph(int c); int islower(int c);int isprint(int c); int ispunct(int c);int isspace(int c); int isupper(int c);int isxdigit(int c); int tolower(int c); int toupper(int c);

6. Example: Reverse a string Given a string str then write a function or a program to reverse that string. Input: str - string Output: reverse – string. Making a string requires: 1. Find the length of the string if possible. 2. Populating the characters. for(i=0;i<length;i++) { str[i] = a char value. } 3. terminating the string with \0 str[length] = ‘\0’;

7. Example: Reverse a string How to do it? 1. Traverse the string reverse forward and the string str backward simultaneously take the current character from str and place it in reverse for(i=0, j=length-1;i<length;i++, j--) { reverse[i] = str[j]; } 2. Terminate the string reverse. reverse[length] = ‘\0’;

8. Example: Counting spaces Given a string str then write a function or a program to find the number spaces are in the string. [It is a counting problem] Input: str - string Output: nr – int. How to do it? • Initialise nr = 0. • Traverse the string and test if the current character is a space repeat for i=0, 1, …, strlen if str[i] is space then nr++;

9. Example: Counting spaces int count_space (char * str) { int nr, i, length; length = strlen(str); nr = 0; for(i=0;i<n;i++) { if(isspace(str[i])) { nr++; } } return nr; }

10. To do List • Solve the HW problems.